1. Field of the Invention
The present invention relates to a method for manufacturing a wet type friction material, particularly used in a wet type clutch.
2. Related Background Art
In automatic transmissions of vehicles, for example, motor vehicles, a multi-plate clutch or a lock-up clutch has been used, and wet type friction materials have been used in frictional engagement elements for such a clutch. FIG. 3 is a front view of a friction plate used in a multi-plate clutch. The friction plate 1 is constituted by adhering wet type friction material(s) 3 to one side or both sides of a core plate 2.
The wet type friction material 3 is generally produced by making paper comprised of fiber base material such as natural pulp fibers, organic synthetic fibers or inorganic fibers and filler/friction adjusting agent such as diatom earth or cashew resin in a wetting manner and then by immersing resin binding agent comprised of thermosetting resin into it and by thermosetting it.
There are various thermosetting resin materials, and such resin materials have been developed more and more, but they have inherent merit(s) and demerit(s).
Therefore, an object of the present invention is to provide a method for manufacturing a wet type friction material, in which demerit of one binding agent is compensated by the other binding agent thereby to provide excellent effect. More specifically, an object of the present invention is to suppress weakness or tenderness which is demerit of silicon resin by using phenol resin while maintaining elasticity or flexibility which is merit of the silicon resin and high coefficient of friction accordingly, and to provide a method for manufacturing a wet type friction material in which tenderness is suppressed.
To achieve the above object, the present invention provides a wet type friction material having fiber base material, filler and binding agent and comprising a first layer including first binding agent and a second layer including second binding agent.
Further, the present invention provides a method for manufacturing a friction plate obtained by fixing a wet type friction material to a core plate, in which the wet type friction material includes a first layer immersed by phenol resin and a second layer immersed by phenol resin and silicon resin and the first layer side is secured to the core plate and the second layer side is used as a frictional engagement surface.
Further, the present invention provides a method for manufacturing a wet type friction material obtained by immersing binding agent into a paper body comprised of fiber base material and filler, comprising a first immersing step for immersing first binding agent into the paper body, a second immersing step for immersing second binding agent into the paper body after the first immersing step, and heating and curing step for heating and curing the paper into which the first and second binding agents are immersed.
In order to manufacture the wet type friction material according to the present invention, a paper body is firstly formed. The paper body is formed by making paper, in normal manner, from slurry liquid obtained by dispersing fiber base material and filler/friction adjusting agent into water at a predetermined ratio and drying the paper. The paper body is not limited to the above-mentioned one.
As the fiber base material, for example, one or more of inorganic fibers such as glass fiber, rock wool, potassium titanate fiber, ceramic fiber, silica fiber, silica/alumina fiber, calion fiber, bauxite fiber, kayanoid fiber, boron fiber, magnesia fiber, metallic fiber and the like and organic fibers such as link pulp, wood pulp, synthetic pulp, polyester fiber, polyamide fiber, polyimide fiber, polyvinyl denaturation alcohol, polyvinyl chloride fiber, polypropylene fiber, polybenzo imidal fiber, acrylic fiber, carbon fiber, phenol fiber nylon fiber, cellulose fiber, aramid fiber and the like may be used.
As the filler/friction adjusting agent, for example, one or more of barium sulfate, calcium carbonate, magnesium carbonate, silicon carbide, boron carbide, titanium carbide, silicon nitride, boron nitride, alumina, silica, zirconia, cashew dust, rubber dust, diatom earth, talc, calion, magnesium oxide, molybdenum disulfide, nitrile rubber, acrylonitrile butadiene rubber, styrene butadiene rubber, silicon rubber, fluororubber and the like may be used.
Phenol resin is used as the first binding agent. The phenol resin is not particularly limited, but, for example, pure phenol resin or epoxy denaturation phenol resin may be used.
Silicon resin is used as the second binding agent. Cured material of hydrolysis liquid of silane coupling agent is used as the silicon resin. The hydrolysis liquid of silane coupling agent can be obtained by pouring silane coupling agent (as main material) and water (and solvent, if necessary) by mixing and agitating these substances for a predetermined time period (for example, about 3 to 5 hours) under a room temperature or a relatively low temperature (lower than boiling point of the solvent (low class alcohol); for example, about 40 to 50xc2x0 C.).
The silane coupling agents having the following chemical formulae (1) and (2) were used.
(R1)(R2)nSi(OR3)3xe2x88x92n xe2x80x83xe2x80x83(1 ) 
(In the above formula, R1 represents alkyl-amino group having first class amine at its end, R2 and R3 represent alkyl group having independent carbon number of 1 to 3, respectively, and n is the integral number of 0 or 1)
(R4)mSi(OR5)4xe2x88x92nxe2x80x83xe2x80x83(2) 
(In this formula, R4 and R5 represent alkyl group having independent carbon number of 1 to 3, respectively, and m is the integral number of 1 or 2)
In the mixture of the silane coupling agents, silane coupling agent having three or more hydrolysis groups is used as at least one of the silane coupling agents represented by the formula (1) or (2). In the hydrolysis liquid of silane coupling agent, it is preferable that blending is effected so that ratio of molar number of the silane coupling agent shown by the formula (2) with respect to molar number of the silane coupling agent shown by the formula (1) becomes 0.1 to 10. Further, in the hydrolysis liquid of silane coupling agent, it is preferable that an adding amount of water is greater than an amount by which half or more of hydrolysis groups in the silane coupling agent an be subjected hydrolysis and smaller than twice of an amount by which all of hydrolysis groups in the silane coupling agent can be subjected to hydrolysis.
More specifically, in the silane coupling agent shown by the above formula (1), as amino silane having three alkoxy group within one molecule, 3-amino propyl trimethoxy silane, 3-amino propyl triethoxy silane, N2-(amino ethyl) 3-amino propyl trimethoxy silane and the like can be listed up, and one of them or mixture thereof can be used. Further, as amino silane having two alkoxy group within one molecule, 3-amino propyl methyl dimethoxy silane, 3-amino propyl methyl diethoxy silane, N-2-(amino ethyl) 3-amino propyl methyl dimethoxy silane, N-2-(amino ethyl) 3-amino propyl methyl diethoxy silane and the like can be listed up, and one of them or mixture thereof can be used.
On the other hand, in the silane coupling agent shown by the above formula (2), 3-functional methyl trimethoxy silane, 3-functional methyl triethoxy silane, 2-functional dimethyl dimethoxy silane, 2-functional dimethyl diethoxy silane can be listed up, and monomer thereof or low compression substance (for example, about 2 to 5 parts) of one or more mixture thereof can be used. Further, silane coupling agent having three or more hydrolysis groups is used as at least one of the silane coupling agents shown by the formulae (1) and (2). It is preferable that the silane coupling agents are compounded so that a ratio of molar number of the silane coupling agent shown by the formula (2) with respect to molar number of the silane coupling agent shown by the formula (1) becomes 0.1 to 10. If the ratio between the molar numbers is below 0.1, since dimensional stability of the wet type friction material is worsened by moisture/water absorbing action due to hydrophilic ability of the cured material, it is not preferable. On the other hand, if the ratio between the molar numbers exceeds 10, since permeating/wetting ability to the base material paper is worsened and physical strength of the wet type friction material is reduced, it is not preferable.
The amount of water to be added is preferably selected so that it is greater than an amount by which half of hydrolysis groups (alkoxy groups) in the silane coupling agent can be subjected to hydrolysis and smaller than twice of an amount by which all of hydrolysis groups in the silane coupling agent can be subjected to hydrolysis, and, more preferably, so that it is grater than an amount by which half of hydrolysis groups (alkoxy groups) in the silane coupling agent can be subjected to hydrolysis and smaller than an amount by which all of hydrolysis groups in the silane coupling agent can be subjected to hydrolysis. If the water amount is below such amount, many non-reacted alkoxy groups will remain in the hydrolysis liquid to worsen the curing ability, which is not preferable in the view point of productivity and energy saving. On the other hand, if the water amount is too much, excessive water will remain in the hydrolysis liquid. The excessive water may cause a phenomenon that density of resin component is increased from interior toward surface layers during the heating and curing, with the result that content of the cored material becomes uneven along the thickness direction of the friction material, thereby affecting a bad influence upon physical strength and friction property. If the adding amount of water exceeds twice of the amount by which all of hydrolysis groups (alkoxy groups) can be subjected to hydrolysis, since excessive water will remain in the hydrolysis liquid, which causes the above-mentioned phenomenon, it is not preferable. If the adding amount of water exceeds the amount by which all of hydrolysis groups (alkoxy groups) can be subjected to hydrolysis, since excessive water will remain in the hydrolysis liquid, although the abovementioned phenomenon occurs, the extent of the phenomenon is within an allowable range. When the adding amount of water is below the amount by which all of hydrolysis groups (alkoxy groups) can be subjected to hydrolysis, since the amount of water remaining in the hydrolysis liquid is small and a uniform material can be obtained, it is more preferable.
Although the solvent is not always inevitable, the solvent is usually used to uniformly mix amino silane and water in the starting mixture liquid, and it is preferable that density of the amino silane in the starting mixture liquid is diluted below 80 weight % by low class alcohol such as methanol, ethanol or propanol. If the density exceeds 80 weight %, binding reaction of silanol groups produced by hydrolysis will be advanced, which may deteriorate storage stability of the hydrolysis liquid.
Phenol resin (constituting the first binding agent) and amino silane (constituting the second binding agent) hydrolysis liquid are immersed into the paper body by an amount corresponding to 20 to 120 weight parts with respect to the base material of 100 weight parts. Then, after dried, heating and curing is effected at a temperature of about 100 to 300xc2x0 C. for 15 to 30 minutes, thereby obtaining the wet type friction material. Then, the wet type friction material is punched as a part having a predetermined shape, and the part is integrated with a substrate (core plate) on which adhesive is coated, by a heat pressing technique, thereby obtaining the friction plate. The manufacture of the friction plate is not limited to the above method, but other method may be used.
By the hydrolysis, the silane coupling agent (amino silane) is changed to compound including silanol group and amino group in the same molecule, in which condensation polymerization between silanol groups is suppressed due to bipolar ion structure of the molecule based on the amino group, thereby providing relatively stable solution. Since this hydrophilic compound having low molecular weight well permeates into capillary spaces of the paper base material and then the silanol groups repeat the condensation polymerization to create siloxane bonding thereby increasing hardness, the organic and inorganic components in the paper base material are coupled together strongly, thereby providing physical strength greater than that of the phenol resin. Further, the cured material has siloxane bonding (xe2x80x94Oxe2x80x94Sixe2x80x94Oxe2x80x94) as main skeleton, and, in the siloxane bonding, since a bonding distance between silicon atom and oxygen atom is long and electron density is low, rotation of binding can easily be performed, and the cured material is very flexible and soft. When the cured material of the hydrolysis liquid of such amino silane is used binding agent for the wet type friction material, due to increase in softness, a contact area of the surface of the friction material is increased, and a burnt mark (called as xe2x80x9cheat spotxe2x80x9d) of the other friction material (separator plate) due to local abutment can be eliminated. Further, initial fluctuation of coefficient of friction is small, thereby realizing high and stable coefficient of friction. Further, bonding energy of Sixe2x80x94O in the siloxane bonding is 106 Kcal/mol, which is considerably greater than 85 Kcal/mol which is bonding energy of Cxe2x80x94C forming the main skeleton of organic resin such as phenol resin. Since such bonding energy is great, even when the cured material of hydrolysis liquid of amino silane is held under a high temperature for a long time period, the cured material is not deteriorated (decomposition and/or discoloration) and becomes stable with respect to frictional heat generated between frictional sliding surfaces, and the wet type friction material has good heat-resistance and endurance.